1. Field of the Invention
The present invention relates generally to an image forming apparatus including a flash fixing unit and, more particularly, to an image forming apparatus including a flash fixing unit with a uniformized fixing energy.
2. Description of the Related Art
A flash fixing method is known as a method capable of performing non-contact fixing in an electrophotographic apparatus. The flash fixing method is capable of fixing a toner image onto a sheet at a high speed and is therefore utilized in the high-speed electrophotographic apparatus. According to this flash fixing method, if a sheet feeding speed is low, a single piece of flash lamp may be enough for the fixing. Whereas if the sheet feeding speed is high, however, three or more flash lamps are needed as the case may be.
FIG. 13 is an explanatory diagram showing the prior art.
As illustrated in FIG. 13, four pieces of flash lamps 90-1 through 90-4 are arranged in parallel to a sheet 92. These flash lamps 90-1 to 90-4 are covered with a reflection plate 91.
The flash lamps 90-1 to 90-4 flash at a constant interval. The sheet is consecutively fed corresponding thereto. Accordingly, an area where the flash lamps effect the fixing at one time varies depending on the number of the flash lamps installed. For this reason, if the sheet feeding speed increases, the one-time fixing area expands. This requires a plurality of flash lamps.
In such a conventional flash fixing unit using the three or more flash lamps, the respective flash lamps 90-1 to 90-4 flash under the same conditions. More specifically, input energies (input voltages) of the flash lamps 90-1 to 90-4 are the same, and installation intervals of the flash lamps 90-1 to 90-4 are made constant.
According to the prior art, however, first, the three or more flash lamps flash under the same conditions, and, hence, as illustrated in FIG. 13, a fixing energy distribution thereof rises in the vicinity of central portion but is lowered at both ends. Therefore, an ill-fixed state is easy to occur at both ends of a fixing area. This results in a ununiformity in terms of the fixing.
Second, the center of the fixing energy distribution is higher than an energy needed for the fixing, and hence there is caused a drop in fixing efficiency.